In 3GPP Long Term Evolution/3GPP Long Term Evolution Advanced (Long term evolution/Long term evolution-advanced, LTE/LTE-A), with a continuous and rapid increase in a quantity of antennas at a data transmit end, a quantity of user equipment (User equipment, UE) that needs to be served, that is, a quantity of to-be-scheduled UE, also rapidly increases. The increase in the quantity of antennas may provide space freedom of a higher degree, which creates a favorable condition for multiplexing multiple data flows in downlink space (which may be (Single-user Multiple-input Multiple-output, SU-MIMO) or (Multi-user Multiple-input Multiple-output, MU-MIMO)).
To acquire space freedom of a high degree that can be provided by massive antennas, related channel state information (CSI) must be acquired by the data transmit end (which is generally a base station), so as to acquire precise precoding (precoder). When MIMO is being performed, in the prior art (for example, LTE/LTE-A), the data transmit end generally acquires the CSI by using two methods:
In one method, in a case of time division duplexing (Time division duplexing, TDD)/frequency division duplexing (Frequency division duplexing, FDD), the data transmit end sends a pilot for CSI downlink measurement, a data receive end (which is generally UE) measures the pilot to acquire CSI, the UE then feeds back the CSI (which is generally quantized CSI and is PMI+RI in LTE), and the data transmit end performs precoding on data by using the CSI and sends precoded data. In the other method, in a case of TDD, a data receive end sends a pilot (for example, an SRS in LTE/LTE-A) for CSI uplink measurement, the data transmit end performs uplink channel CSI measurement, the data transmit end considers that the uplink channel measurement is a downlink channel according to channel reciprocity (a necessary reciprocity parameter is generally required for modification), and then performs precoding on data according to the CSI and sends precoded data.
A volume of downlink pilot overheads is proportional to a quantity of antennas at a data transmit end, a volume of uplink pilot overheads is also proportional to a quantity of to-be-served UE, and a quantity of uplink CSI feedbacks is also proportional to the quantity of antennas at the data transmit end. Therefore, when the quantity of antennas at the data transmit end is not very large (for example, 4/8 antennas in LTE/LTE-A), pilot overheads and a quantity of uplink CSI feedbacks can be controlled; however, when the quantity of antennas is relatively large (a quantity of UE that can be scheduled also increases), uplink and downlink pilot overheads and a quantity of uplink CSI feedbacks occupy a large quantity of time-frequency resources, which results in reduced compresses time-frequency resources available for data transmission, thereby greatly affecting a system throughput.